Thin-film magnetic discs or media are widely used as data storage media for digital computers. The discs are typically formed by successively sputtering onto a rigid disc substrate, an underlayer, a magnetic layer, and a carbon overcoat which protects the magnetic layer against wear and reduces frictional forces between the disc and a read/write head.
It is also common to lubricate the disc, in a final surface treatment, with a thin film of a fluorocarbon lubricant, to reduce frictional interactions between the head and the disc, particularly during start/stop cycles. Standard lubricants for this purpose are perfluoropolyether oils, such as "AM 2001" or "Z-DOL" lubricant supplied commercially by Ausimont (Morristown, N.J.).
The lubricity properties of discs are generally measured in terms of dynamic and/or static coefficients of friction. Dynamic friction coefficients are typically measured using a standard drag test in which the drag produced by contact of a read/write head with a disc is determined at a constant spin rate, e.g., 1 rpm. Static coefficients of friction (stiction values) are typically measured using a standard contact start-stop (CSS) test in which the peak level of friction is measured as the disc starts rotating from zero to a selected revolution rate (e.g., to 5000 rpm). After peak friction has been measured, the disc is brought to rest, and the start-stop process is repeated for a selected number of start-stop cycles. One important property of a disc which is required for good long-term disc and drive performance is that the disc retain a relatively low coefficient of friction after many start/stop cycles or contacts with a read/write head. For example, a drive manufacturer may require that the disc have an initial stiction value of no greater than 0.3, and a stiction value of no greater than 1.5 or 2 after 20,000 start/stop cycles. A disc that meets such a specification can thus tolerate at least 20,000 start/stop cycles without exhibiting high friction characteristics that would deleteriously interfere with read/write operations.
Heretofore, the most commonly employed lubricants used with magnetic media, and particularly the perfluoropolyether class of lubricants, have been found to perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Thus, it has been necessary to use temperature and humidity control systems to avoid less favorable environmental conditions which would otherwise cause a rapid reduction in disc performance.
Accordingly, there is a need for improved lubricant compositions which are able to provide good frictional properties not only under ambient conditions, but under conditions of higher temperature and high or low humidity as well.